What Was the Common Language of Communication in India?

Okcostob: Before english, you had french as the diplomatic language in the west. So even to day, in diplomacy, the knowledge of frenchs is quitea common and pprevalent. And you also do find people with blondish, brown hair, or blondish hair, even red hair. It's quite rare, but it is there. All these genetic mixes, components, are prevalent to various degrees in india too. Okcostob: What was the common language for communication between two linguistic between two?